Jose Mourinho has defended Paul Pogba's sluggish start to his second spell at Old Trafford, stating the world-record fee paid for him by Manchester United is not a "big deal" in relative terms.

Pogba left United for Juventus in 2012 but returned in August in a transfer costing an initial £89million, making him the most expensive player in the world.

After impressing on his debut against Southampton last month, the France international came under fire for disappointing displays in defeats to rivals Manchester City and Feyenoord.

United this week reported a club-record £515.3m revenue for the last financial year, and the Portuguese suggested such financial muscle makes other clubs paying £40m for a player more surprising.

"I think there are clubs that paid 20, 30, 40 [million pounds] which is a bigger deal than what Man United paid for Paul," said Mourinho, who takes his side to Watford on Sunday.

"When you make a relation between what you pay and the club revenue, you realise that other clubs paying 20, 30, 40 is a much bigger thing than what Man United did. I just want Paul to forget that and play his football."

Mourinho is unsurprised that Pogba has been unable to make a significant impact yet, but backed him, and his team-mates, to come good soon.

He continued: "[Pogba was in the] Euro final, no pre-season, holidays. He had a very good impact in the first game, but it's normal that after the first game he has a little decrease.

"But I'm full of trust with him because I know the player he is, I know he's a very good guy with a lot of ambition so the form will come naturally and will come with the team. The team improves, Paul improves, so no problem."

Pogba played as one of a midfield two against Southampton but was part of a trio in the centre against Feyenoord, though Mourinho does not believe there is any issue with finding his best position.

"He can play where he was playing before in the Premier League, he can play where he did [against Feyenoord], there's not a problem with his position," added the Portuguese.

"It depends on the situation. In the Premier League we were playing with Wayne Rooney as a number 10, and y we played with Schneiderlin in front of the back four [against Feyenoord] and we gave him [Pogba] more freedom to occupy other kind of spaces."